1. Field of the Invention
This invention relates to a process for producing a urea-formaldehyde condensate-based slow release nitrogen fertilizer which, after application to the soil, is capable of releasing nitrogen into the soil for a prolonged period of time to enable advantageous cultivation of plants.
2. Description of Prior Art
Methods for using urea-formaldehyde condensates as a nitrogen fertilizer are known. For instance, Japanese Patent Publication No. 1,166/71 proposes a method which comprises foaming a urea-formaldehyde resin by use of a foaming agent in an appropriate foaming apparatus, crashing the resulting foamed cured product into fine grains with a size of 0.1 to 20 mm by a crasher, adding water thereto to form a slurry, mixing the resulting slurry with plant seeds, etc., and applying the resulting mixture to the soil. Also, Japanese Patent Publication No. 56,517/82 discloses a method which comprises reacting urea with formaldehyde in a urea : formaldehyde molar ratio of 1:2 to 2.5 to form methylolurea or a urea-formaldehyde precondensate of such a condensation degree that the condensate is substantially soluble in water, then adjusting the obtained reaction mixture to a pH of 3 to 7 and spray-drying the same at a temperature of 200.degree. to 400.degree. C. to produce fine hollow spheres of urea resin having a specific partial water solubility, and using the fine hollow spheres as a slow release fertilizer.
However, none of the conventional ureaformaldehyde condensate-based slow release fertilizers including those exemplified above are suitable as a slow release fertilizer, because these conventional fertilizers have such problems as quick conversion into an inorganic substance, inhibition of the germination of seeds and the like. Also, many of the processes for preparing such conventional fertilizers are complicated.